There is an increasing interest in the use of organic field effect transistors (OFET) where an active channel of the transistor is made from an organic material. To be useful, the organic material must be capable of supporting a channel of holes or electrons when the device is switched on by applying a voltage to a gate associated with the channel. Moreover, the carrier or field effect mobility of the organic material must be sufficient to facilitate a large increase in conductivity between the source and drain when the device is on versus off.
The active channel in conventional OFETs is composed of organic molecules, such as polymers or oligomers, having conjugated bonds. For instance, overlap between pi-orbitals of adjacent organic molecules allows the channel to be conductive. In some cases, doping, by either removing (via oxidation) or inserting (via reduction) electrons into the organic molecule, can improve their conductivity. Approaches to improve the carrier mobility of the channel include hydrogen bonding columnar stacks of organic molecules together and preparing alignment layers for organic molecules on the substrate. Nevertheless, existing OFETs continue to have channel regions with low carrier mobility and hence poor sensitivity, due in part, because of the small difference in the drain current in the “on” versus “off” state.
Accordingly the present invention overcomes the disadvantages associated with prior art devices by providing an OFET having a channel whose carrier mobility is higher than previous OFETs and a method for the fabrication of such a device.